A stent is a tubular medical device which is used for therapy or treatment of various diseases arising from stenosis or occlusion of a living body lumen such as a blood vessel and, specifically, is set indwelling (i.e., is indwelled) in the stenosed part or occluded part so as to dilate the part and secure the lumen thereof. Since a stent is inserted into the living body from the outside, it is reduced in diameter at the time of insertion and, thereafter, it is expanded or restored to an enlarged diameter state in the target stenosed or occluded part, so as to secure the lumen while remaining in the enlarged diameter state. Stents are classified into self-expandable stents and balloon-expandable stents, depending on their function and manner of expansion. A balloon-expandable stent is a stent which itself does not have an expanding function; the stent mounted on a balloon is inserted into the target part, and thereafter the balloon is inflated to expand (plastically deform) the stent by the balloon's expansive force, thereby fixing the stent in close contact with the inner surface of the target lumen.
This type of stent needs the above-mentioned stent-expanding operation. On the other hand, a self-expandable stent is formed from a material having shape memory properties, and is produced in the size of an expanded final shape. In order to introduce a self-expandable stent into a living body, the stent in a small folded state is inserted into a member (mostly, a plastic-made tube) for restricting its shape, is then introduced into the living body together with the member, or tube, and is released from the tube at the target part, whereon the stent self-expands by its shape memory properties.
At present, the mainstream of self-expandable stents are stents formed in a substantially cylindrical hollow shape by interlinking at joints a plurality of annular bodies which are each formed in a substantially zigzag pattern by interconnecting a plurality of strut sections with a plurality of loop sections.
The self-expandable stent disclosed in WO 96/26689 (hereinafter referred to as Patent Document 1) has a structure in which wavy annular bodies are interconnected by connectors which are formed obliquely.
In addition, there are stents of the type in which vertexes of a meandering element or zigzag element enter into the adjacent meandering element or zigzag element. An example of this type of self-expandable stent includes the one disclosed in WO 97/32546 (hereinafter referred to as Patent Document 2). In the self-expandable stent disclosed in WO 99/65421 (hereinafter referred to as Patent Document 3), vertexes of the adjacent meandering elements as above-mentioned are interconnected by connectors parallel to the stent axis.
In addition, there are stents of the type in which meandering elements or zigzag elements are not in a plane loop form but in a spiral form. Examples of this type of stents include one composed of one or a plurality of spiral elements extending from the distal end to the proximal end thereof. For example, according to WO 98/30173 (hereinafter referred to as Patent Document 4), zigzag elements are interconnected by connectors parallel to the stent axis, for maintaining the shape of the stent. Further, as self-expandable stents in which adjacent annular bodies are partly integrated with each other by a shared linear section, the present inventors have proposed those disclosed in EP 2098195 A1 (hereinafter referred to as Patent Document 5), U.S. Pat. No. 7,651,524 B2 (hereinafter referred to as Patent Document 6) and U.S. Pat. No. 7,618,445 B2 (hereinafter referred to as Patent Document 7).
Stents are desired to have good compressibility permitting compression to an outside diameter as small as possible, a sufficient expansion-retaining force when expanded, and good trackability with respect to deformations of a living body lumen such as a blood vessel.
The stents of the types disclosed in the above-mentioned Patent Documents 1 to 4 have been insufficient in trackability with respect to deformations of a blood vessel, though sufficient in the expansion-retaining force. In addition, although the stents of the types disclosed in Patent Documents 5 to 7 have good effects, there is a demand for a stent which has better compressibility and better expansion-retaining force and trackability with respect to deformations of a blood vessel.